The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.
Pumping stations 2 for emptying sewage wells (FIG. 1a) and filling water wells (FIG. 1b) are known. As shown in FIG. 1a, waste water and sewage is supplied to the well 4 via an inlet 7 and the pumps 10 are configured to empty the well 4. In contrast, FIG. 1b shows that water drains from the water well via outlet 9 and the pumps 10 are instead configured to fill the well 4.
These pumping stations 2 include the well 4 in which liquid 6 is located, a level sensor 8 for sensing the liquid level in the well 4, a pair of pumps 10a, 10b for pumping liquid into or out of the well 4 as required, and a controller (not shown) in communication with sensor 8 and for controlling the operation of the pumps 10a, 10b based on the sensed liquid level in the well 4. FIG. 1 shows various level trigger-points along the level sensor 8 in the form of liquid sensing electrodes. The controller independently activates or de-activates the pumps 10a, 10b with hysteresis in response to it sensing the liquid level via the electrodes.
The controller can display the instantaneous output flow rate of the pumps 10 upon a display which a pumping station supervisor can monitor. The instantaneous flow rate can be sensed using a flow meter, however, such sensors are undesirably expensive. As a cheaper alternative, the flow rate for each pump cycle can instead be estimated.
A known flow rate estimation method is now briefly described with reference to FIG. 1a. The inflow rate (I) through inlet 7 can be readily determined, when the pumps 10 are deactivated, as follows:
                    I        =                              Δ            ⁢                                                  ⁢                          V              well                                            Δ            ⁢                                                  ⁢            t                                              (        1        )            where ΔVwell is the change in liquid volume in the well 4 that can be measured using liquid sensor 8 and Δt is the change in time.
Upon activation of one or both of the pumps 10, the output flow rate (F) of the pumps 10 can be determined by the following equation:
                    F        =                                            Δ              ⁢                                                          ⁢                              V                well                                                    Δ              ⁢                                                          ⁢              t                                +          I                                    (        2        )            where the inflow (I) is measured once immediately prior to the activation of the pumps 10. However, the inflow (I) may be prone to variation during a pump activation cycle. Therefore the output flow rates of the pumps can instead be determined by averaging a number of prior calculations of the flowrate.
When the pumps 10 are continuously activated for a long period of time during a pumping cycle, the output flow rate (F) of the pumps 10 can instead be determined, by averaging a number of prior inflow rates (I) determined when the pumps 10 were deactivated, as follows:
                    F        =                                            Δ              ⁢                                                          ⁢                              V                well                                                    Δ              ⁢                                                          ⁢              t                                +                      I            ave                                              (        3        )            where Iave is the average inflow rate determined by averaging a number of previous inflow rates (I) determined in accordance with Eq. 1 (e.g. ten previous inflow rates).
However, the flow rate (F) determined in accordance with Eq. 3 can become inaccurate under certain circumstances including, for example, when the actual inflow rate suddenly changes significantly (e.g. during a downpour). In this event, the displayed flow rate (F) is reduced and the pumping station supervisor cannot reliably ascertain whether a pump 10 is blocked or the actual inflow rate through inlet 7 has increased, which is clearly undesirable.
It is an object of the present invention to provide a method of more accurately determining the output flow rate (F) of the activated pumps than the method described above in relation to Eq. 3.